It is known that CHCl.sub.2 CF.sub.3 and CHClFCF.sub.3 are obtainable in good yields from tetrachloroethylene, a readily available and relatively inexpensive commodity. However, the use of CHCl.sub.2 CF.sub.3 and CHClFCF.sub.3 as starting materials for the production of highly fluorinated hydrogen-containing products (such as pentafluoroethane) by reaction with HF has typically yielded appreciable amounts of perhalo by-products containing chlorine (evidently via side reactions). Undesirable chlorofluoroethanes have been especially noted when attempting to increase conversion to pentafluoroethane by operating at high temperatures. Chloropentafluoroethane (i.e., CClF.sub.2 CF.sub.3 or CFC-115) is an especially deleterious by-product. Not only does it constitute a yield loss of the hydrogen-containing compounds, but it has a boiling point close to that of pentafluoroethane (i.e., CHF.sub.2 CF.sub.3 or HFC-125) with the resulting mix being costly to separate.
U.S. Pat. No. 5,334,787 discloses a process for the preparation of CHF.sub.2 CF.sub.3 by the reaction of a material selected from the group consisting of C.sub.2 HCl.sub.2 F.sub.3 and C.sub.2 HClF.sub.4 with HF, in the vapor phase, and in the presence of a solid Cr.sub.2 O.sub.3 catalyst. Conditions are controlled whereby the formation of CFC-115 and other perhalo derivatives is minimized, and the examples illustrate obtaining CF.sub.3 CHCl.sub.2 hydrofluorination products containing 1% or less, for each of CF.sub.3 CH.sub.2 F, CClF.sub.2 CHF.sub.2, CF.sub.3 CH.sub.2 Cl, CF.sub.3 CCl.sub.2 F, CClF.sub.2 CClF.sub.2, CF.sub.3 CClF.sub.2, CF.sub.3 CCl.sub.3, CClF.sub.2 CCl.sub.2 F and CClF.sub.2 CHClF (not all of these by-products are reported for each example). While the process illustrated in this patent represents a useful way of obtaining low amounts of perhalogenated ethane by-products, even the low amounts illustrated cause difficulties in purification. Accordingly, there is still a desire for processes which can provide pentafluoroethane in high yield with even lower production of perhalogenated impurities (especially C.sub.2 Cl.sub.2 F.sub.4 and C.sub.2 ClF.sub.5).
Pentafluoroethane is useful as a blowing agent, propellant, refrigerant, fire extinguishing agent, sterilant carrier gas, or heavy gas for an aerodynamic wind tunnel. It is desirable for its zero ozone depletion potential.